Reconcile with vegan

Currently `R CMD check`  fails in `envfit.coca`. The new `getPermuteMatrix`  interface needs `strata = NULL` if there are no strata.

I don't know if we can fix this in **vegan**, so it is probably best to fix it here (although there is another CRAN package that fails with the same).

You also need some more imports from **vegan** NAMESPACE.